An ultrasonic flaw detection test, as one of ultrasonic measurement tests, is known as a test in which an ultrasonic beam is transmitted from a surface of a test piece to the inside thereof to detect an ultrasonic echo reflected due to a flaw existing inside the test piece and thus estimate a size of the flaw from the loudness of the echo returned, while an amount of time elapsed from the transmission of an ultrasonic wave to the reception of the returned wave is measured to learn a distance to the position of the flaw.
For the purpose of conducting the ultrasonic flaw detection test for the test piece, an ultrasonic probe, acting as an ultrasonic transmitting and receiving unit, is employed. One end of a waveguide rod is allowed to contact with the probe via a liquid contact medium, while a contact surface of the other end of the waveguide rod is allowed to contact with a surface of the test piece via a liquid contact medium. An ultrasonic sound wave emitted from a vibrator of the probe travels in a straight line inside the waveguide rod and then reflects off a boundary surface of the flaw existing inside the test piece. Then, the ultrasonic wave, being an echo thus reflected and returned from the boundary surface, is received by the probe. The position of the flaw can be detected based on differences in time taken from the transmission of the ultrasonic waves to the reception thereof, and even if the test piece is at a high temperature, the flaw detection test can be conducted (e.g., refer to patent document 1).
In this manner, employing the waveguide rod enables diagnoses to be performed for in-service equipments such as steam pipes in electric power plants with which no probe is allowed to directly contact as well as for parts that are being processed and may reach a high temperature during their production processes.
According to the conventional art described above, however, employing the waveguide rod has caused such problem that a noise echo (sometimes, referred to as a trailing echo) obtained by the probe becomes too large. Specifically, unwanted noise echoes arise which interfere with the flaw detection by the reflection and mode conversion of an ultrasonic wave on a columnar surface of the waveguide rod.
As discussed above, according to the conventional waveguide rod, noise echoes arise on the columnar surface of the waveguide rod due to the reflection and mode conversion of an ultrasonic wave. Particularly, when an ultrasonic wave is emitted from the central position of the waveguide rod whose cross-sectional shape is circular, echoes, which have repeated the reflections and the mode conversions on the columnar surface, return to the probe, causing the noise echoes to arise. These noise echoes pose a major impediment to a pulse echo method used frequently for the ultrasonic flaw detection and hence it is craved to eliminate or alleviate the noise echoes.
Referring to the above patent document 1, it is disclosed therein that a waveguide rod comprises an externally threaded portion, a straight columnar portion, a right circular truncated cone portion and a plurality of independent minute depressions or protrusions formed on an outer circumferential surface of the right circular truncated cone, whereby ultrasonic waves inside the waveguide rod that do not enter a test piece are allowed to reflect off the depressions or the protrusions in a turbulent state, thereby preventing them from returning to a probe, thus reducing the loudness of the noise echo, i.e., the energy level thereof. Patent document 1: Japanese patent publication No. 3587555